The mineralogical basis for understanding biohydrometallurgical processing of low-grade
sulphide ores and means by which microwave processing improves their microbial
recovery is investigated using a Nigerian low-grade complex sulphide ore as a case study.
The study is approached through an applied mineralogical study of the ore and its
influence on developing an optimal route for the microbial leaching of the low-grade
complex ore under varying process parameters, and an investigation on the interaction
between mineralogy, microwave processing and bioleaching. Bioleaching behaviour,
mechanisms of bioleaching, and the interplay of mineralogy and microwave irradiation
and their influence on bioleaching process were carried out using mixed cultures of
Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillium ferrooxidans in a
mechanically stirred glass reactor at varying bioleaching process parameters and through
electrochemical studies. Mineralogical analysis of the ore revealed the presence of siderite,
sphalerite, galena, quartz, and traces of pyrite and chalcopyrite, with the ore exhibiting fine
to coarse grain intergrowths of the constituent crystalline phases both at the interstitials
and the boundaries. Complexity in the mineralogy of the ore affected mineralogical and
elemental distribution amongst varying size fractions that led to variation in the galvanic
behaviour within these size fractions and influenced microbe-mineral’s reactivity and the
different dissolutions behaviours. Bioleaching at optimal bioleaching parameters revealed
the highest dissolution at a particle size fraction of 75 μm, while electrochemical studies
revealed the highest dissolution at particle size fraction of 106 μm. This discrepancy was
consistent with and attributed both to the physical and mineralogical influences. The
combined effects of mineralogical variation, precipitation phenomenon as well as the
physico-chemical effect of particle size, controlled bioleaching behaviour, while galvanic
interaction resulting from variations in mineralogical distribution controlled the
electrochemical behaviour. Ore mineralogy and microwave heating both showed dual
influences on heating characteristics, size reduction, and the effectiveness of microwave
treatment in improving dissolution. The increase in the dissolution rate and the overall
dissolution of the microwave treated samples is attributed to phase changes in the ore
which promoted galvanic interaction within the system, decrease in the amounts of sulphur
contents, and an increase in electrochemical and microbial growth sites resulting from an
increase in the number of cracks induced by microwave heating.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/5981 |
| Date | 28 January 2009 |
| Creators | Olubambi, Peter Apata |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf |
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